1. Field of the Invention
The present invention relates to a radio telephone apparatus which performs radio communications, more particularly to a power-saving control of a transmitted output in the radio telephone apparatus.
2. Description of the Related Art
A power-saving control of a transmitted output typified by a PHS radio telephone apparatus has been heretofore performed by limiting a dynamic range of a detection circuit provided therein. However, the method to limit the dynamic range of the detection circuit has been able to lower the transmitted power by 15 to 20 dB at most.
Accordingly, when a power-saving control exceeding 20 dB is required, a method has been employed, in which a fixed bias voltage is applied to a voltage control variable attenuator constituted by a pin diode and the like provided in a RF stage of a transmission system, and the power source of a driver amplifier is cut off, whereby a gain of the transmission system is lowered and the transmitted output is set to a predetermined power-saving output.
However, in the foregoing power-saving control method in the conventional radio telephone apparatus, during the power-saving control, an auto power control circuit (hereinafter, referred to as an APC circuit) in which a feedback loop is formed is in an OFF state, so that there is a problem that a variation in a gain of amplifier in the transmission system owing to an ambient temperature change directly becomes a variation in the transmitted output, and a stable transmitted output cannot be acquired.
Moreover, when a temperature compensation for the foregoing transmitted output is conducted, there is a problem that a circuit structure becomes complicated.
The present invention was made in consideration for the problems involved in the foregoing conventional arts, and the object of the present invention is to provide a radio telephone apparatus which is capable of obtaining a more stable transmitted output.
In order to achieve the above described object, a radio telephone apparatus of the present invention comprising:
an antenna for receiving and transmitting a radio wave;
receiving means for extracting a specified signal from the received radio wave through the antenna;
transmitting means for transmitting information to be transmitted to the outside through the foregoing antenna; and
control means for outputting a control signal for lowering the transmitted output of the transmitting means by a specified amount, thereby controlling the transmitted output of the transmitting means,
wherein the foregoing transmitting means comprises:
modulation means for modulating the signal to be transmitted through the foregoing antenna;
variable attenuating means for attenuating the signal modulated by the modulation means based on the control voltage inputted and outputting the attenuated signal;
amplifying means for directly outputting the signal inputted from the variable attenuating means when the control signal is outputted from the control means, and amplifying the signal outputted from the variable attenuating means to output the amplified signal when no control signal is outputted from the control means;
detection means for demodulating the signal inputted from the amplifying means, and detecting a detection voltage by different circuits depending on whether or not the control signal is outputted from said control means, based on an output of the control signal from the control means;
reference voltage generating means for generating different reference voltages depending on whether or not the control signal is outputted from said control means, based on an output of the control signal from the control means; and
comparing means for comparing the reference voltage with the detection voltage detected by the detection means, thereby a comparison result, and
wherein the variable attenuating means attenuates the signal modulated by the modulation means, using the control voltage based on the comparison result from the comparing means.
The radio telephone apparatus of the present invention is characterized in that a counter is provided, which performs a counting operation based on the comparison result outputted from the comparing means and outputting a counted value, a D/A converter is provided, which converts the counted value outputted from the counter to an analog signal, and the variable attenuating means attenuates the signal modulated by the modulation means, using the analog signal outputted from the D/A converter as the control voltage.
The radio telephone apparatus of the present invention is characterized in that the detection means includes two resistors having different resistivities from each other, and switches the detection voltage to be inputted to the comparing means by selectively coupling the comparing means with one of the two resistors based on the output of the control signal from the control means.
The radio telephone apparatus of the present invention is characterized in that the detection means has two directional couplers exhibiting different degrees of coupling, and switches the detection voltage to be inputted to the comparing means by selectively coupling the comparing means with one of the two directional couplers, based on the output of the control signal from the control means.
In the radio telephone apparatus of the present invention constructed as described above, the signal to be transmitted through the antenna is modulated by the modulation means provided in the control means, the signal modulated by the modulation means is attenuated by the variable attenuating means based on the control voltage inputted thereto, the signal attenuated by the variable attenuating means is amplified for its power by the amplifying means and outputted therefrom, the signal outputted from the amplifying means is demodulated by the detection means and the detection voltage is detected by the detection means, the detection voltage detected by the detection means is compared with a previously determined reference voltage by the comparing means, and the signal modulated by the modulation means is attenuated by the variable attenuating means based on the comparison result by the comparing means. Hereupon, the signal outputted from the variable attenuating means is directly outputted from the amplifying means when the control signal is outputted from the control means, and the signal outputted from the variable attenuating means is amplified for its power by the amplifying means and outputted therefrom when the control signal is not outputted from the control means. Furthermore, the detection means is constructed such that the detection voltage to be detected differs depending on the presence of outputting of the control signal from the control means.
As described above, the detection voltage is switched depending on the presence of outputting of the control signal from the control means and a feedback loop for controlling a transmitted power based on the comparison result of the detection voltage with the reference voltage is provided, so that a constant transmitted output can be achieved stably both at the times of a rated output and the power-saving control.